Fiberglass covered trilam

[LaBill67]

Guys I'm about to start on a trilam bow and would like some opinions on my planning at this stage.  The fiberglass I've already ordered is Bo-Tuf .040 glass for the back and belly. The bow itself will be a R-D design using hard maple parallel lams at .125 back and .094 belly.  The core will be IPE starting at .375 at the fades tapering to .063 at the ends.  I'm hoping to get a bow weight of approximately 45-50 pounds.  Overall length to be 68" with a riser length of 19".  Bow width to be 1.5" at end of fades and tapering to 5/8 at the tips.  I will really appreciate any inputs you may have regarding this plan.

[Robertfishes]

Total stack of 0.674, sounds a bit too much. Since you are using 040 glass back and belly I would call this build a D/R longbow or maybe a hybrid longbow. Depending on design I would think some where closer to 0.380 total stack height? You might want to use all maple laminations with a total taper of 003/inch..again taper depends on the bow design.

[LaBill67]

Thanks Robertfishes for your input.  Any thoughts on how you would vary the lams to achieve your recommended overall thickness?

[Robertfishes]

The only D/R longbow I build is the original KennyM design. I have built more than a dozen, mostly 66" long.  Kenny might be able to calculate the stack height for his design. I have not looked at my build book to see what the 50 lb stack height is..  If I were building a 0.380 thick bow based on that design...I would use two 090 001/inch tapers on back side of bow, one 060 001/inch taper and one 060 parallel on the belly side of riser. The 060 pieces will bend up the riser ramp nicely. So your stack would be 040 glass, 090 taper, 090 taper, riser, 060 taper, 060 parallel, 040 glass. Total stack in center is 0.380

[kennym]

I think .674 will be an elephant killer , at least on my form. On my design, using .003 total taper and 18" riser, .380-.385 total would be my guess.

Think Robert has it nicely. But, would need to see the form to be sure. 1" extra reflex on my 64" made 5# extra with same stack, so the first one is a SWAG.  

[mikkekeswick]

Yeah don't make a wood bow and add glass! It would be well over 100# @ that stack! Also use low sg woods for the core. On a glass bow the core is just a spacer to get the glass faces the correct distance apart and as such low density is a very good thing, ipe is best kept for the belly of wood bows or use it in the riser.

[LaBill67]

Hmm, so Mikkekeswick, are you saying it doesn't matter what the core is when using glass front and back?  If that's the case what thickness of glass and core would you recommend or is the weight dependent on the design of the form as Kennym seemed to indicate?

[BMorv]

Bill, I can't believe you are ditching us all wood guys so soon!    :(
 
From what I gather, fiberglass bow building is a game of design, precision, and trial an error.  I would stick to a proven design with known lam and taper thicknesses for your 1st one.  From there you can play around with different materials and designs.  A search through Kenny's post is probably where I would start.  
Just my 2 pennies.

[Robertfishes]

Core wood does matter...ever seen a balsa wood bow? The core wood still has to be able to flex with out shearing or breaking. You should Stay with the proven laminated bow woods like hard maple and red elm..I use laminated bamboo (actioboo) most of the time, bamboo is a grass not wood but makes a nice bow limb lamination.

[LaBill67]

BMorv don't worry I'm not ditching all wood bows at all; just trying my hand at other projects.  I have several pieces of pecan I harvested from a tree my dad had on his place.  I cut, quartered, and put aside the pecan back in August.  So until that dries I need something to work on and decided to give fiberglass a try.  I also have some 4" diameter bamboo drying in the loft of my shop I hope to use later on.  So you can see I've not ditched all wood bows.  But for now I'm into this and must see it through.  Thanks to all for your inputs and suggestions.  I really do appreciate your advice.

[kennym]

Hey Bill,

There are stacks on here to look over.....

 http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=011684#000010

Good luck and we like pics!  

[LaBill67]

Kenny, thanks a lot for the link and I will certainly upload some pictures as I go along.  
I am currently fine tuning my form and these plans will be very useful as I go about doing that.

[LaBill67]

I have pretty well completed my form thanks to Kenny. Now my next question concerns the pressure strip, at least that's what I think it's called.  I picked up two pieces of 1/8" x 36" aluminum yesterday.  I had read where the 1/16" was too thin. After I got it home I discovered the curve on another riser handle I built was maybe too concave and may require a load of pressure to get the aluminum to bend into it.  So, the question is do I make the curve on the fades to handle the pressure strip or just go ahead and force the pressure strip into the curve?

[LaBill67]

Never mind guys, I got my answer.  Seems pretty simple now that I really think about it.

[Robertfishes]

I have only used galvanized metal pressure strips. They can be bought from some of the trad gang sponsors.

[LaBill67]

What adjustments if any do any of you make to account for the fact that the arrow shelf is cut above center?